Question

once a preganglionic axon reaches a trunk ganglion, one of three things can happen to the axon. which of the following is not one of these three things?
the axon can ascend or descend the sympathetic trunk to synapse in another trunk ganglion.
the axon can course back into the spinal cord to synapse with preganglionic neurons in a different spinal segment.
the axon can pass through the trunk ganglion and emerge from the sympathetic trunk without synapsing.
the axon can synapse with a ganglionic neuron in the same trunk ganglion.

Explanation:

To solve this, we recall the fate of preganglionic axons in the sympathetic trunk: 1) Synapse in the same trunk ganglion. 2) Ascend/descend to synapse in another trunk ganglion. 3) Pass through the trunk ganglion without synapsing (to synapse in a collateral ganglion). The option "The axon can course back into the spinal cord to synapse with preganglionic neurons in a different spinal segment" is incorrect because preganglionic axons do not return to the spinal cord to synapse with other preganglionic neurons—they synapse with ganglionic (postganglionic) neurons or pass through.

Answer:

The axon can course back into the spinal cord to synapse with preganglionic neurons in a different spinal segment.